Actin protein is a highly abundant protein in eukaryotic cells and plays a critical role in various cellular functions. Actin exists in two forms, Globular Actin (G-actin) and Filamentous Actin (F-actin). G-actin is the monomeric, soluble form of the protein, while F-actin refers to the polymerized, filamentous structure. Actin filaments form a dynamic cytoskeleton that provides structural support, enables cell motility, and supports muscle contraction. In muscles, actin molecules twist together to form thin filaments, which interdigitate with thick filaments composed of myosin, the most abundant protein in muscle. When a signal for muscle contraction is sent along a nerve to a muscle cell, actin and myosin are activated. Myosin acts as a motor, hydrolyzing adenosine triphosphate (ATP) to release energy, which causes a myosin filament to move along an actin filament, resulting in the sliding of the two filaments past each other. Actin filaments are highly concentrated at the cell periphery, forming a three-dimensional network beneath the plasma membrane. This network, composed of actin filaments and associated actin-binding proteins (known as the cell cortex), determines cell shape and is involved in various cell surface activities, including movement.
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